We had this one hour radio show discussing the topic two days ago, with guest American legal experts on it (plus one specialist of American politics). They specifically discussed the angle of "national security" as the host brought it up (he asked specifically if the US government could invoke these laws to censor sites like Wikileaks last year, if it provided the US with new legal tools to deal with cyber-terror or other cyber-threats to national security). The experts all agree: that's totally outside the scope of those laws, and they also agreed those laws don't touch on matters of national security at all. Those new laws as they stood were designed specically to adress piracy and breaches of commercial and corporate copyrights in answer to the demands of Hollywood (that financed Obama's campaign) and the videogame industry. One of the lawyers said fears your governement could use PIPA or SOPA to deal with sites like Wikileaks were unfounded (what Wikileaks published isn't even copyrighted or proprietary material). Under PIPA/SOPA, they can't "close down a foreign website" anyway. All they can do is make its DNS unreachable directely. It would be a child's game to reach the site nonetheless (you just need to know it's IP address which would become widely known very rapidly), it just wouldn't show up anymore in search tools like Google and company. The US don't have the technical means to totally shut down a site like Wikileaks outside the US, and SOPA/PIPA don't give it those means.

Beside, the felony in Wikileaks' case was committed by the American guy who leaked the material, not by Wikileaks, a foreign site with foreign proprietors, that bought and published it, nor the worldwide media that relayed the information from Wikileaks (including the New York Times, officially a media partner of Wikileaks, that wasn't charged with anything....). If the US prosecutors thought they had grounds to charge Assange with anything, they would have tried to get him extradited (which could have been complicated, given a great deal countries including your closest allies won't extradite anyone to the US if he faces the death penalty, and I'm pretty sure it includes Australia) but it appears Assange hasn't broken any American law anyway.